Temperament and mental illnesses are considered to be varying degrees along the same continuum of imbalance in the neurophysiological regulation of behavior. Mental disorders are linked to specific patterns in the relationships between neurotransmitters and between brain structures. Similar links were found for temperament traits. Development of DSM and ICD classifications might benefit therefore from an integration between psychiatry, functional neurochemistry and differential psychology.

To describe the neurochemical systems underlying mental disorders and temperament traits in healthy adults.

Findings in neurochemistry, neuropsychology, differential psychology and psychopathology are compared to the traits described in various temperament models. This analysis is summarized in the perspective of the neurochemical functional ensemble of temperament (FET) model.

Neurochemical correlates for 12 main dynamical aspects of behavior are presented as a systemic framework that follows a universal functional structure of human actions described in kinesiology, neuroanatomy, neurochemistry and clinical neuropsychology. The role of monoamine systems (serotonin, dopamine, noradrenalin), acetylcholine, GABA/glutamate, neuropeptide and opioid receptor systems are linked to regulation of specific dynamical properties of behavior in a systematic way. Several insights for the structure of the classification of mental disorders from the perspective of the FET model are proposed.

An integration of research in neurochemistry and psychopathology of behavior with differential psychology based on healthy samples can bring new insights for future versions of DSM and ICD classifications of mental disorders. Such integration does not follow either dimensionality or categorical approach but instead is based on functional ecology of human behavior.